Devices of this type are used in particular in the corrugated cardboard industry where it is important to establish an equilibrium of humidity on the one hand between the single-sided sheet formed by sticking a sheet of corrugated paper to a web of smooth paper and on the other hand the covering constituted by another web of paper intended to be stuck to the second side of the corrugated sheet in order to produce a double-sided sheet, if one wishes to eliminate warping of the product obtained, i.e. a transverse deformation of the latter due to the appearance of tension between the single-sided sheet and the covering at the time of the hot connection of the latter.
Naturally, this constitutes only a non-limiting example of an application to the extent that the same problem occurs each time two webs of hydrophilic material have to be connected and undergo, at the time of their connection, in particular if the latter takes place hot or after this connection, a treatment tending to dry them and consequently to cause a deformation of the product obtained in the case where its two constituents would tend to be subjected to different dimensional variations at the time of this drying.
Normally, humidifier devices comprise, opposite the path of at least one of the sides of at least one of the webs, an arrangement for spraying water directed transversely with respect to the direction of travel of the web and comprising a plurality of jets distributed over the width of the latter. For example, in the case of a machine for manufacturing corrugated cardboard processing webs of paper having a width of 2.45 meters, 12 jets are thus distributed over the width of at least one of the webs.
The rate of flow through each of the jets may be regulated independently, presently by rotating graduated knurled wheels provided at the rate of one per jet, in order to control the rate of flow through this jet through the intermediary of suitable means. Thus, depending on the transverse deformation which the finished product tends to undergo, i.e. for example the corrugated cardboard, the operator regulates the flow through the various jets by a suitable rotation of the corresponding knurled wheels, in order to supply the web with humidity modulated over its width and thus to establish an equilibrium between the respective rate of humidity of the respective areas of the two webs intended to come into contact with each other, in order that they undergo indentical dimensional variations upon drying, with the result of a flat finished product.
Generally, the two connected webs are subjected to a treatment of this type.
Generally, this regulation is effected once and for all at the beginning of the travel of a web of predetermined origin and is maintained during the passage of the entire length of the web. Nevertheless, it proves difficult, long and tedious, in particular in that it is difficult to establish a direct relationship between the graduations on the knurled wheels and the deformation observed on the finished product, depending on which one must regulate the rate of flow of the various jets by a suitable rotation of the knurled wheels.